The present invention relates to crosslinkable waterborne polymer compositions suitable for coatings. In particular, the present invention relates to waterborne compositions encompassing a functional latex polymer containing an ethylenically unsaturated moiety, a silicon hydride material and a catalyst suitable for reaction of the silicon hydride with the functional latex polymer.
The increased awareness of the effects of volatile organic solvents on the environment is causing a re-evaluation of the use of solvents in coatings. As a result, many coatings manufacturers are switching from organic to water based coatings systems. The typical strategy used to produce waterborne coatings which form hard, tough films, has been to produce an emulsion polymer with a glass transition temperature (Tg) above room temperature and plasticize this polymer with a solvent to lower the Tg of the polymer and thereby reduce the film formation temperature of the latex. The solvents used to lower the glass transition temperature of the polymer are known in the industry as coalescing aids. The coalescing aids present in a typical thermoplastic paint composition increase the volatile organic content (VOC) of the paint.
An alternative way of producing a coating having hardness and toughness properties is to produce a latex with a Tg below room temperature which is capable of forming a film at room temperature, and then crosslinking the film to give film toughness and solvent resistance properties. In the published literature, there are many examples of curing chemistries that have been applied to solvent based systems. However, chemistries suitable for solvent based systems are not always applicable to waterborne systems.
The application of hydrosilation reactions in crosslinking silicon polymer systems is well known in the literature. An article published by Batch et al. in Rubber Chem. Technol., 64(2), 218-33 (1991) describes the hydrosilation reaction as applied to silicon systems. Also a review of this technology can be found in Silicone Rubber in Powder Form, Swanson, Leicht & Wegener, Amer. Chemical Society, Rubber Div., October 1974. Applications of this chemistry to non-silicon systems is limited.
EP Application 94109495.5 discloses a curable resin composition containing a homo- or copolymer of an organohydrogenpolysiloxane macromonomer, an allyl group containing polymer and a hydrosilation catalyst. The above patent, however, teaches melamine resin compositions which are not waterborne and does not refer to the use of hydrosilation chemistry in curing waterborne latex polymers.
U.S. Pat. No. 5,321,082 describes curable resin compositions comprising a polymer having a plurality of alkenyl groups, an organohydrogenpolysiloxane, a polymer having a plurality of alkenyl groups and a hydrosilation catalyst. This patent does not refer to compositions that cure waterborne latex polymers.
U.S. Pat. No. 4,962,165, refers to a process for making silicon-containing polymer particles by a suspension polymerization. The polymer particles of this patent are prepared by polymerization of functionalized silicon-containing material, containing at least one copolymerizable functional group per siloxane chain. The functionalized siloxane-containing material is then suspension polymerized to form crosslinked silicon rubber particles. The functionalized siloxane-containing material of this patent may alternatively be copolymerized with active surfactants by suspension polymerization or coated or encapsulated with other copolymerizable unsaturated monomers, as by an emulsion copolymerization, after the silicon-containing material has been crosslinked to modify the surface properties of the siloxane-containing material. The '165 patent however, does not use hydrosilation reactions as a method of controlling crosslinking reactions since the particles in the patent are pre-crosslinked.
EP 0 702 068 A1 Application refers to a method of forming multilayer coatings on a substrate such as automobile bodies. The method of EP 0 702 068 A1 Application comprises the steps of applying a pigmented basecoat composition onto the substrate, applying a clear topcoat composition onto the basecoat and curing both coats individually or simultaneously. The clear topcoat composition comprises a resin having pluralities of both hydrosilyl groups and alkenyl groups in the molecule, or a blend of resins having a plurality of hydrosilyl groups in the molecule with a resin having a plurality of alkenyl groups in the molecule. In addition the method of the EP 0 702 068 A1 Application requires a catalytically effective amount of a hydrosilylation catalyst. None of the compositions are waterborne latex polymers.
EP 0 602 933 A2 refers to a hydrosilylative composition comprising an acrylic polyester or epoxy resin having at least two alkenyl or alkynyl groups in a molecule, and an organic silicon compound having at least two hydrogen atoms each directly attached to a silicon atom in a molecule, a hydrosilylation catalyst, and at least one of an organic iron compound and an organic aluminum compound. None of the compositions are waterborne latex polymers.
EP 0 566 095 A1 and corresponding U.S. Pat. No. 5,321,082 refer to a curable resin composition containing a polymer having a plurality of alkenyl groups, and organohydrogenpolysiloxane having a plurality of hydrosilyl groups, a polymer having a plurality of alkynyl groups, and a hydrosilylation catalyst. The composition of the patents is stable at room temperature but is crosslinkable at an elevated temperature. None of the compositions are waterborne latex polymers.
EP 0 450 844 A2 refers to a curable resin composition which comprises an organic resin containing at least two alkenyl groups per molecule and having a specific molecular weight, and organohydrogen polysiloxane containing no less than two Si--H bonds per molecule and a platinum catalyst. The organic resin is preferably chosen from at least one of acrylic, polyester and epoxy resins. The compositions of this patent can be cured at low temperatures without shrinking to give a product having good water resistance, chemical resistance and recoatability. None of the compositions are waterborne latex polymers.
U.S. Pat. No. 5,539,073 describes the production of waterborne polymers that contain pendant allyl groups. The patent further describes the oxidative cure of such latexes with metal driers, but does not teach the use of hydrosilation reactions.
The prior art does not disclose any waterborne crosslinkable polymer compositions which may be cured using a hydrosilation reaction. Thus, there still exists a need for waterborne polymer compositions suitable for crosslinking by hydrosilation, without the use of coalescing agents or other compounds contributing to the volatile organic content (VOC).